Large second-order nonlinearity in poled fused silica.

Area of Science:

• Nonlinear Optics
• Materials Science
• Photonics

Background:

• Second-order nonlinear optical effects are crucial for photonic devices.
• Fused silica is a common optical material but lacks intrinsic second-order nonlinearity.
• Previous methods for inducing nonlinearity in silica have limitations in stability or magnitude.

Purpose of the Study:

• To induce a significant and stable second-order nonlinear optical susceptibility (χ(2)) in fused silica.
• To investigate the process parameters and stability of the induced nonlinearity.
• To explore potential mechanisms responsible for the observed nonlinear effect.

Main Methods:

• Commercial fused-silica optical flats were subjected to a thermal poling process.
• Temperatures ranged from 250-325°C with applied electric fields of approximately 5 x 10⁴ V/cm.
• The induced nonlinearity was characterized and tested for stability and cycling.

Main Results:

• A large second-order nonlinearity (χ(2) ~ 0.2 pm/V) was successfully induced in the near-surface region (4 µm).
• The induced nonlinearity is significantly larger (10³-10⁴ times) than that observed in fiber-based experiments.
• The nonlinearity demonstrated high stability at room temperature and could be repeatedly cycled (poled and depoled) without history effects.

Conclusions:

• Thermal and electric-field poling is an effective method for creating large, stable second-order nonlinearities in fused silica.
• The induced nonlinearity is robust and can be controllably programmed, opening possibilities for optical device fabrication.
• Further research into the underlying mechanisms, such as nonlinear moieties and electric-field-induced effects, is warranted.